The present disclosure relates to a solid-state imaging device having a global shutter structure.
Shutter methods for image sensors (solid-state imaging devices) include a rolling shutter method in which rows are exposed to light sequentially from an upper one to a lower one, and a global shutter method in which all rows are simultaneously exposed to light. For CMOS solid-state imaging devices, the rolling shutter method has been widely adopted. However, a solid-state imaging device having a rolling shutter structure causes image distortion (so-called focal plane distortion) when capturing the image of an object moving at a high speed.
In view of this problem, CMOS solid-state imaging devices with a global shutter structure have been proposed recently. In such a solid-state imaging device having the global shutter structure, memories are formed on a semiconductor substrate, apart from photodiodes. Signals are simultaneously read from all the photodiodes to the memories, and then, the signals are sequentially read out from the memories. In this manner, an image without distortion can be captured. For this reason, it is required to employ the solid-state imaging devices with the global shutter structure as industrial cameras that need to identify an object moving at a high speed, high-end cameras, and similar cameras.
On the other hand, in order to obtain high-quality images without increasing the size of the solid-state imaging device, the size of each of cells included in the solid-state imaging device tends to be reduced. However, as the cell size is reduced, it becomes difficult to condense light that has entered in the cell. It is therefore needed to realize a high-sensitivity solid-state imaging device capable of efficiently collecting incident light despite a decrease in the cell size.
Japanese Unexamined Patent Publication Nos. H11-040787 and 2006-73882 each describe a solid-state imaging device including an intra-layer lens provided above a plurality of wiring layers and covering a region above a photodetector, and an on-chip lens provided above the intra-layer lens. In the solid-state imaging device described in each of these patent documents, the incident light condensed by the on-chip lens is more effectively collected to the photodetector by the intra-layer lens having a substantially hemispherical shape which is upwardly convex.
Japanese Unexamined Patent Publication No. 2008-192951 describes a solid-state imaging device including an optical waveguide disposed between a photodetector and an intra-layer lens and penetrating a plurality of wiring layers. In the solid-state imaging device described in this patent document, since light that has entered the optical waveguide is guided to the photodetector while being confined in the optical waveguide, the light-gathering efficiency is improved.